Vertical angles are pairs of angles that are opposite each other when two lines intersect. Here's a step-by-step explanation to determine the number of pairs of vertical angles:
1. When two lines intersect, they form two pairs of vertical angles.
2. Each pair consists of two angles that are congruent (equal) to each other.
3. Therefore, for every intersection of two lines, there are 2 pairs of vertical angles.
In conclusion, when lines intersect, there are always 2 pairs of vertical angles formed.
